Pallets made of thermoplastic materials are rapidly replacing old wood-type pallets. The plastic pallets have been proven to be lightweight, resilient, inexpensive to manufacture, and can easily be configured in different shapes due to their molded construction.
One disadvantage that plastic pallets have relative to wood pallets is that the plastic pallets are more susceptible to creep. Even at relatively low temperatures, such as 80.degree. F. to 120.degree. F., the permanent deformation of the plastic pallets under load can be significant.
Pallets are often stacked one atop another resulting in primarily compressive loading. In other instances, pallets may be stored in racks. The racks have opposing ledges upon which laterally spaced edge portions of the pallets are placed. Accordingly, the central spans of the pallets are left unsupported. If the temperature in the surroundings in which the pallets are stored becomes sufficiently high, and the pallets are kept on the racks for an extended period of time with heavy loads thereon, these pallets can exhibit significant deformation due to creep. Consequently, the center of the pallets may sag downwardly with the laterally spaced and supported edge portions moving inboard toward one another. If the edge portions move sufficiently inboard, the edge portions may slip from the rack with the pallet falling therefrom.
One solution to this sagging and creep problem for edge or simply supported pallets is to provide rigid steel bar reinforcements in the pallets to reduce the amount of sag. The steel bars use their inherent structural rigidity to act as beams resisting vertical deflection due to the vertical loads placed on the pallet. The rigid reinforced pallets thereby decrease the overall amount of sag or vertical deflection as compared to a pallet without the reinforcement.
However, pallets with the rigid reinforced steel bars therein have a number of shortcomings. A first problem is that the steel bars can become permanently deformed thus permanently deforming the overall pallets. Occasions where steel reinforcement bars may become bent include when the pallets are dropped, run over by a truck or other vehicle or else run into by a forklift. In these cases, the steel bars and surrounding pallets may have permanent, and often undesirable, deformations formed therein.
Another problem is that using thick steel bars with substantial cross-sectional area to provide stiffness against lateral deflection or bending also significantly increases the overall weight of the pallet. One of the chief advantages of using plastic pallets is that they are lightweight. Hence, using thick steel bars offsets this advantage.
An additional problem associated with insert molding rigid steel bars within pallets is that the steel bars have a propensity to work their way through the plastic. Ends of the rigid bars can then protrude through external surfaces of the pallets. The protruding bars may snag objects or make otherwise flush surfaces bulge.
The present invention is intended to minimize the shortcomings associated with pallets which are reinforced with rigid steel bars.